For the month of September, the weather has become unusually active over the past ten days with the spectacular lightning storm of Sept. 7 followed by several other weather systems in the days following.
And we're not quite done yet!
Another compact area of low pressure -- modest for the fall windstorm season but rather potent for September -- is taking shape in the Gulf of Alaska Monday morning. These areas of cold low pressure are rainmakers, but they also make the atmosphere more unstable. Colder air aloft will move along with this weather system. When this cold pocket of air upstairs in the atmosphere is much colder than normal, warmer pockets air at the surface is able to rise more quickly and higher in the sky. This forms taller rainclouds. When instability is great enough, thunderstorms can erupt with even some small hail!
As the Alaskan weather system moves toward us, a weaker area of low pressure will depart. Still, colder air aloft combined with warming surface temperatures in the afternoon will probably produce enough instability for a few thunderstorms in the lowlands Monday afternoon into Monday evening. %
The lightning will be nowhere near as frequent as weekend before last (a truly-astonishing event we'll likely not see again for many years.)
Still, get inside if thunderstorms approach! You can track the storms with lightning plots on the KIRO 7 Pinpoint Weather App.
When the stronger Alaskan weather system actually pulls into our region Tuesday morning, a band of heavy rain will spread across the Northwest for several hours, tapering to more scattered showers around early afternoon.
Winds just off the surface associated with this system will be rather strong, and some of that wind will impact the surface with gusts in the 25-35 mph range from the morning into the early afternoon. A few gusts will probably be recorded over 40 mph in a few more favored lowland locations, like across the islands of the north and right on Puget Sound. %
This brief burst of windy weather likely won't be enough to produce widespread problems but just like on any breezy day, a few power outages and branches and limbs down can be expected.
Beyond Tuesday, we can expect more tranquil weather for the remainder of the week and into the weekend with the next weather system of note arriving sometime around Sunday. Right now, the longer-range outlooks do NOT point to major fall-like nasty weather continuing for the remainder of the month. We'd sure like some time to dry out!
Our consistently-active period of wet and windy weather usually arrives in full form in October or early November. I expect that this year too.
Just like with anything in weather or the environment, the answer is usually "some" or "a little."
Very rarely (almost never!) is something
responsible for a particular result -- in this case, a weather event. %
But the area of warmer-than-normal Pacific waters -- the so-called "Blob" -- has surely boosted our local temperatures a little recently. Probably a degree or two warmer overall but we really don't know for sure.
Any warming of the lower levels of the atmosphere would increase the instability when these low pressure systems with their cold air aloft move overhead. How much? Again, we don't know for sure but we're confident in saying "some."
Remember, colder air aloft over warm air at the surface is a more unstable condition, leading to more storm clouds, heavy rain and lightning.
The astonishing amount of lightning on Saturday night, Sept. 7 was likely boosted somewhat because of the "Blob."
Estimating just how much is probably a great research project for the fine students of atmospheric science at UW!
Is the "Blob" going to be around all winter? Probably not -- at least not to the magnitude of warmth right now.
The "Blob" formed because of persistent high pressure over the eastern Pacific during the spring and early summer months. The air above the water was warmer than usual and the water also wasn't churned up or cooled by passing weather systems. So it got much warmer than normal.
As our fall weather systems take shape with more frequency, expect the "Blob" to cool somewhat or possibly even go away by winter.
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